Multi-scale Groundwater Numerical Simulation Of Kun-cheng Tunnel Of Water Diversion Project In Kun Ming Crossing Black And White Karst Pipeline In Cheng Gong Area

The current popular groundwater numerical simulations are mostly based on equivalent continuous medium generalizing water-bearing medium.However this method is not absolutely applicable for karst region,especially the karst region in southern China where karst pipeline is highly developed and the water-bearing medium is composed of fissures,solution fissures and pipes,making the groundwater flow forms both laminar flow and turbulence flow.Equivalent continuous medium can not reflect that groundwater flow feature,so it is now a difficult problem for researchers to make a breakthrough on reflecting karst pipeline medium feature in groundwater numerical simulations.This paper relies on KunMing-ChengGong tunnel of water diversion project in KunMing,using Visual-Modflow to set up multi-scale groundwater flow model.Large scale model provides the boundary conditions and hydrogeological parameters to small scale model.Within the small scale model which generalizes water-bearing medium as equivalent continuous medium,ChengGong black and white karst pipelines are generalized by module River.Karst pipelines are analyzed by the multi-scale numerical models,and combining with KunMing-ChengGong tunnel crossing through black and white karst pipeline systems to study of groundwater dynamic characteristics,and predict the recovery of groundwater seepage field after tunnel construction.The main results and conclusions are as follows:?1?Black and white karst pipeline systems share one supply source but divide to two independent systems.The supply source is the exposed karst band in the northeast part of study area.Obstructed by aluminum clay rock of P₁d,groundwater is divided into two parts during the runoff process.There is no direct hydraulic connection between these two karst pipeline systems,and the water level of White karst pipeline system is higher than Black karst pipeline system.?2?During the tunnel construction process,the water level of White karst pipeline exit reduce 9m in pipe model B₁ while the solution fissure model B₂ reduces 10m,both two models suggest that the tunnel construction will cause the unwatering of White karst pipeline exit.The water level of black karst pipeline exit reduce 1m in pipe model B₁ while the solution fissure model B₂ reduces 4m.The setting of karst pipeline causes the change of water exchange between aquifer and pipeline,the original form that aquifer supplies pipeline turn into pipeline supplies aquifer while the water level reduces caused by tunnel construction.This change makes model water level reduce degree is lower than model B₁.?3?In model B₁,tunnel construction total water discharge is 69876m³/d,in model B₂,the number is much larger than model B₁ for the quick groundwater transport and exchange by karst pipeline,total water discharge is 95817 m³/d.?4?After tunnel construction and blocking up,the water level of two pipeline exits and observation well start to recover,the recovery trend is relatively rapid in the early stage,and later is relatively slow.It takes 8.5 years for the black and white pipeline exits to reach the original water level,and 10 years for observation wells.During the recovery process,groundwater exchange form change from pipe supplying aquifer to aquifer supplying pipe,which makes model B₂ recovers faster than model B₁ in early stage,and the opposite in later stage.?5?Using large scale model combining with secondary scale model,and the module River generalizing karst pipeline can reflect the flow dynamic characteristics of karst pipeline effectively.